I was having troubles getting fetch() to post, the remote server (Twitter, in this case) complained at me that their "resource only supports POST". Turned out to be a known bug in OAuth 1.1, downgrading to 1.0 fixed it.

So I'm using this to talk to the Woocommerce REST API, and was having a lot of trouble figuring out what exactly $extra_parameters was supposed to look like (which WC REST API expects, besides being of the type OAUTH_AUTH_TYPE_URI).

The multidimensional array I fed it crashed PHP, so don't do that if you're in my shoes.

What ended up solving it was me looking through the OAuth source and noticing that $extra_parameters can also be a string, which, encoded as json (json_encode), solved all my troubles as WC accepted it.

If the provider's web server is configured to use Keep-Alive extension to HTTP protocol (HTTP 1.1), there can be a big delay in the response time from the provider. By default Apache is configured to use Keep-Alive for 5 seconds. This is the delay after which the response will come back to the consumer. If you have this issue of delayed result, you can pass in HTTP headers when calling $consumer->fetch():

Then the provider will send the result immediately after it's ready with the processing and the connection will be closed. Unfortunately, when calling $consumer->getRequestToken() and $consumer->getAccessToken() there's no way provided to pass in HTTP headers and this delay (if present) cannot be avoided, or at least we could not find a way to avoid it.

The solution that worked for us is to send this header from the provider when returning result to the consumer:

This can work if you have the possibility to modify the code of the provider, e.g. if you are the provider yourself or if you can talk with the people that develop it and ask them to send this header for your request.